Embodiments of the invention particularly concerns an injection nozzle intended for use in cylinder lubrication of engine cylinders in large diesel engines, particularly marine engines. In such systems, the injection nozzle may include a dosing unit. In such lubricating systems, the injection nozzle has previously been intended for introducing an injection jet in the form of oil mist lubrication. Disclosures of examples of this technique are known e.g. from WO 00/28194, WO 02/35068 and WO 04/038189, which publications are hereby incorporated by reference.
Such an injection nozzle may optionally include a dosing unit or be adapted as an injection nozzle without dosing in the nozzle itself. The term “injection nozzle” thus covers a machine part extending through the cylinder wall and connecting a nozzle outlet or oil injection orifice at an end inside the cylinder with oil connection openings on a part outside the cylinder wall.
Several examples of injection nozzles of the type mentioned in the introduction are known. The injection nozzle is connected with a supply source for oil which is sprayed under pressure into the interior of the cylinder at a given time adapted to the work stroke of a piston in the cylinder.
The injection nozzles are disposed in a number around the circumference of a cylinder. The injection nozzles are usually disposed in radially or largely radially oriented mounting holes in the cylinder wall and extend through this cylinder wall. The injection nozzles are fastened to the cylinder wall via mounting means, e.g. by screw thread on the valve stem itself, or by a mounting bushing screwed into threaded holes formed in the cylinder wall.
The injection nozzles are provided with one or more nozzle outlets that are transversely oriented relative to the nozzle rod and are directed in a direction desired for the actual mounting hole for providing lubrication/flushing with a desired orientation inside the cylinder.
The above mentioned valves have the function that the closing element/valve body moves backwardly against the flow of the introduced oil.
However, injection nozzles where the valve body moves forward with the flow of the incoming oil are known as well. This is an advantage for injection nozzles used for injecting lubricating oil under high pressure, so-called SIP-valves. The advantage appears in that a rising pressure in an injection chamber will not influence the closing capability of the injection nozzle in the same way as in the case of injection nozzles where the needle moves backwards, as the closing action is then a balance between the pressure in the oil and the spring pressure plus the pressure prevailing in the injection space/chamber. By rising pressure in the cylinder there will be a risk that the injection nozzle can leak.
The injection nozzles operating with a forward movement with the flow of oil will have valve bodies with inner borings for conducting the oil to a position close to the nozzle outlet for reducing the dead volume, which is particularly important when injecting small amounts of oil to be atomised at the injecting action.
Former injection nozzles are therefore complicated due to the formation of internal ducts.
Moreover, the former injection nozzles are disadvantageous as there may be a blocking of the free movement of the valve body. This problem is particularly seen in connection with injection nozzles where the valve body moves backwards against the oil flow, though occurring in the prior are injection nozzles as well where the valve body moves forward with the flow of the supplied oil. The problem with free movement is caused by the fact that the lubricating oil can contain relatively large particles which are e.g. introduced in the lubricating oil in connection with production/storage/transport of the lubricating oil. These particles have sizes in the magnitude of 6-10 μm. In the former injection nozzles, these particles can be deposited between the valve body and the guide for the valve body, thereby preventing free movement of the valve body.
Examples of injection nozzles for fuel injection by which the valve body moves forward with the flow of oil are known e.g. from GB 610,873 and JP 59-90765.
The difference between injection nozzles for cylinder lubrication and for fuel injection is mainly that pressure, viscosity and dosing amounts differ significantly. An injection nozzle for cylinder lubrication will thus—compared with injection nozzles for fuel injection—deliver substantially lesser amounts at a substantially lower pressure combined with fact that the oil has a markedly higher viscosity. These conditions are to be transferred to a design which is simple and robust.
In practice when working with valve bodies in the form of needles in needle valves, it can be difficult to filter off particles in the lubricating oil with a size down to the typical gap dimension used in needle valves, namely 8-10 μm or less. Typically, central filters are used for the entire lubricating system as local cylinder filters will be difficult to mount and maintain. Typically, there is no problem with filtrating the oil locally or centrally with a filter filtering off particles larger than 0.01 mm. In practice, the experience is typically that a central filter with a mesh size of 0.025 mm or larger can be applied. Such a filtration is sufficient to ensure that clogging of the nozzle outlets in the individual injection nozzles does not occur. In order to prevent possible contaminated oil from blocking or jamming in the gap between the valve body and the valve body guide, a large gap is needed. However, this puts demands on the valve body as larger gaps will make such a valve body unsuitable in use.
Injection nozzles according to embodiments of the present invention can be used for injecting cylinder lubricating oil as a compact jet or by an atomisation of the injected oil. The injection nozzle will typically be adapted for operating at a pressure between 25 and 70 bar, typically at 40 bar or above. As mentioned above, the pressure at injectors for fuel are substantially higher—typically 500-1000 bar.
It is also desired that systems for oil injection can be made with a more simple piping between lubricating apparatus and injection nozzles. This may, e.g. occur by coupling the injection nozzles in series. However, traditional injection nozzles are not suited for such an arrangement.
On traditional injection nozzles, the pressurised oil act on a relatively small annular area, and at the same time relatively long valve guides are used with a small gap up to 0.01 mm. To this is added that the quality of the valve seat with regard to width and surface greatly affects the forces applied on the valve needle at given pressure conditions. This means that crack-pressure can be very uneven. Crack-pressure indicates the pressure at which the valve body begins to move, and the crack-pressure will primarily depend on friction and adherence between valve body and valve housing.
In the former injection nozzles, this means that the force and thereby the pressure required for lifting valve bodies can vary much among individual injection nozzles, and over time for one injection nozzle as well. This has entailed that former injection nozzles have not been suited for coupling in series.